# include <iostream>
# include <vector>
//# include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    while (cin >> n)
    {
//        cout << n * (n + 1) / 2 << endl;
//        cout << endl;
//解决了公式不能过的情况（题目只保证n为int类型，可是等差数列中间值可能会超过int范围）
        if(n % 2 == 0)
            cout << n / 2 * (n + 1) << endl;
        else
            cout << (n + 1) / 2 * n << endl;
        cout << endl;
    }
    return 0;
}
